Self-modulated magnetron



Jan. 6, 1953 A. M. cLoGsToN 2,624,863

SELF-MODULATED MAGNETRON Filed oct. 1o, 1945 IN V EN TOR. ALBERT M GLOGSTON ATTORNEY Patented Jan. 6, 19.53

UNITED STATES' F'FIQEA 2,624,ss3- snLE-Monnmfrsn MAGNnTnoN f Albert Alll/L l Clogston, Melrose, Mass.; fassignor; by mesne assignments, to thje. United"- States-ofi' America asrepresented by the Secretary ofWar Appiicationoetober A1o, 1945;. serialQN'o; 621,565 (c1. sisi-4m.

6 :Claims This invention relates i'rrgeneral to therrnionic` tubeapparatus and more particularly.,to` such apparatus embodying the :so-called magnetron type ofv tube.-

The use of thermionic tubesinv frequencygen--.

erating apparatus .is well known and many such types exist. Therefare times when it .is' desirable.

to vary thefrequency output of a particular tube.

In'some cases this is done by varying .theparameters I the circuits associatedwith thegtubeiin such ,fashion that thenatural period.ofoscilla tion Vthereof-.is changed. Oni the Yother, hand, .it becomes ldesirable for. some uses. ofthetubelto..

have the frequency aiTecting meansincluded within the tube itself and accordingly it 4is' anob-,

ject of my invention to provide'a thermionic tube in which this is accomplished. l Y

One of the tubes whichrv isl found to beof' con-' siderable use, lparticularly for generating the.

higher frequencies, isjthe soeca'lled'magnetron type of tube and when associated"with` apparatus such as radio object locatingjapparatus, itlisj necessary that theV frequency be controlled and` that-some means be provided for Varying. the

natural output frequency; of 'the magnetron ai desi-red manner. Accordingly' it' is another ofthejA objects of my invention-'to provide means-included in the magnetron type *of tube for affectingjand varying `the-output frequencyor the tuberj Apparatus heretoforel known-to i prior art andi associated withi the magnetron 'type of'tu'be have had disadvantages such asV difculty in adjustmen-15;.. maintenance l and-the like! It* is "another netron type of tube- -in which the natural free quency-v outputfth'ereof -may bevarif'e'd'by'-therm-V ionic means associated-with -the tube -itsli-r Inv general my apparatus contemplates-thepr visionfof a pluralityof cathodes Within a'm'agne' thereof` and -is operated `at a, relativelyzlarge .1pc-

tential difference with respect to theanodgfoff;

thetube.asus-usual. Thesecond cathode which ispvidd is operated so that` the...potentia1i,

establishedbetween itself andthe anodel lies iin a region of about half the. potential .established A.

between the Afirst-mentioned catliodegor, as, itv

will .betermedthe main cathode. and the anode'.y

The emission of .electronsfrom the,frcfaquencyai:4 fectirligEor.y secondary cathode into the fringing.

eld ofl theanode results in a change in the ef- 2;. fectiveresonant frequency of the magnetron cavity. The amount .of frequency .'modulation that results from this arrangement will riseas the relative potentialbetween the anode andthe secondary f cathode rises until` the secondary cathode will-tend to take over theradio frequency Figure is. an' elevation sectional view taken' Referringto Figure 1,7 a tubular metal member I2 is closed on top and bottomby the discs Il! and I3.respectively.. Vanes II rigidly attached to the inner walls .of I'Z'gp'roje'ct radially inwardly toward the.` axis' of thelcylinderand constitute the anode.

and 25x aremounted 'end to. end on the `axisrfof the anode. These cat hcdes are of the convene. tional type having theireXte'rioI'- surfaces coated with suitable thermionic material andare provided with heaters. not shown, to providejthe desired ,thermionic emission. A strong' magnetic' lieldisdire'cted along the axis, as shownschef matically. at. |41 and isprodu'c'ed by an external magnet, not shown,` `whose. poles arev in contact with topand bottom discs'lii and I3 respectively. The application of a high voltage. direct current between cathode 20 and the anode, generatesk high frequencyoscillationsin theanode cavities as described later. The function of cathode 25 is `,topfrovide acloud of free.electronsY in the' space. I8 between cathode 25 and theupper edges I'I 'of` the Y. anode vvanes.` The presence -of' these freeelectronsL-in the high vfrequency eld formedbe? tweensthe inner Yedges of thefanode vanes, alters the `resonant.frequencyof the anode cavities. The'cstructure'is shown inv more detail in Figf uresa and;4= where thenumerals .used indicate.

In` Figure .4M which corresponds Yto--Figurel the cathodes .20" and 25-areshown provided with heaters 2.61 and 2'I. v Cathode 20v is supported by4 coaxial line' 36 4andsis.supplied with vheating .current by central conductorv 34` from transformer 3''and source" the same. elementsas in .Figure l.

In the recessiormed between the inner.V ends of thevane's,twov cylindrical cathodes 20`Y 32. Similarly, cathode 25 is supported by coaxial line 31 and is supplied with heating current by conductor 35 from transformer 3| and source 33.

Radial vanes ll attached to cylinder I2 form resonant cavities 43 as is known in the art. A high potential direct current source 38 impresses a negative potential on cathode 20 causing electrons to flow from the cathode to the anode vanes. A magnetic eld parallel to the axis of the cylinder is provided by magnet poles N and S. The electrons leaving the cathode are defiected by the magnetic field into cardioid shaped paths just grazing the vane tips. For simplicity these means paths are shown circular in Figure 3. With this grazing adjustment oscillations are generated in the resonant cavities 43 by the alternate attraction and repulsion of the vane tips as is well known in the art. Useful energy is abstracted from one of the cavities byl magnetic coupling loop 28 and led off by lead 29. The frequency of oscillation is determined by the natural period of the resonant cavity and to some extent by the interaction with the electron cloud in front of the vane tips.

The function of the upper cathode 25 is to provide an additional electron cloud I8 in the space between the upper vane tips I1 and the cathode 25. This electron cloud may or may not engage the vane tips. In either case the free electrons exist in the alternating electric eld between the vane tips. Since electrons have mechanical inertia, the electron motion as is well known lags 90 electrical degrees behind the accelerating and retarding alternating electric elds and constitutes lagging currents in the circuit. In other words the electron cloud acts like inductance introduced in series with the inductance inherent in each cavity resonator and therefore changes the natural frequency. Thus by varying the density of the electron cloud in the interspace IB the frequency of the energy generated by the lower cathode 2D and vane tips I6 may be varied.

The method of varying the frequency is to Vary either cathode voltage as applied by source 39 or by varying the emission by varying the supply of heating current from source 33.

Usually the potential difference between the anode Il and the cathode 25 is in the region of about half the potential established between the anode Il and the cathode 20. It will be appreciated however that this invention is not limited to the particular value of potential.

By way of example, a magnetron operated in a continuous wave fashion and producing an output frequency Whose wavelength was below 100 centimeters having a power output of 1'7 watts produced a frequency shift of megacycles when a power input of 16.4 Watts to the tuning cathode was used.

Referring to Fig. 2, there is shown an alternative form of my invention in which the plural cathodes used are mounted concentrically rather than merely coaxially as shown in Fig. 1. In this showing the cathode which is used to produce radio frequency power is mounted in the space between the vanes as is normal in the art to which this case belongs. The tuning cathode however is mounted in a slot cut in the vanes of the anode as shown in the drawing. Again the tuning cathodes operate in a region of low potential relative to the anode. Electrons emitted by the tuning cathode are caught in the anode fringing field and cause the resonant frequency of the oscillator to change to a degree dependent upon 4 the potential existing between the tuning cathode and the anode. Hence this potential affects the extent of electron emission from the tuning cathode.

By way of example, a magnetron operated in a continuous wave fashion and supplying 32 watts output produces a frequency shift of approxi* mately 51/2 megacycles with a tuning power of 8.4 watts. Accordingly it should be noted that the tuning power required for a given shift in frequency is less where the concentric cathode arrangement is used as it is in the case where the coaxial arrangement of cathode is used.

While examples have been given relatively to the use of the magnetron in a continuous wave fashion, it will be appreciated that the arrangement need not necessarily be operated in that fashion but can be used where pulsed operation is utilized.

It will be obvious that there may be departures from the particular showing as made in this specication which will still fall fairly within the spirit of the invention. One such modification, for instance, may be that the two cathodes need not be mounted exactly coaxially, although this is considered at the present time to be a preferable arrangement. Accordingly, I claim all such modifications as fall fairly within the spirit and scope of the invention as identified in the hereinafter appended claims.

What is claimed is:

1. An oscillation generator of the multicavity magnetron type, two cathodes for emitting electrons mounted on a common axis and in cooperative relation with the respective inner edges of a common radial vane system constituting resonant anode cavities, rst cathode connected to a source of high direct current potential for generating high frequency oscillations in said resonant anode cavities, coupling means for abstracting useful energy from one of said cavities, and electron means for varying the resonant frequency of the cavities, said means including a source of direct current potential connected to second cathode, whereby an electron cloud is formed in the high frequency eld between the second cathode and the inner edges of said vanes.

2. An oscillation generator of the multicavity magnetron type, a single cylindrical anode housing provided with inwardly projecting radial vanes forming a plurality of resonant anode cavities. two cathodes for emitting electrons mounted on a common axis at opposite ends of the interspace between inner edges of said radial vanes, a source of high direct current potential connected to rst cathode coactng with lower edges of said radial vanes to generate high frequency currents in said resonant cavities, magnetic coupling means for abstracting useful energy from said resonant cavity system, and electron means for varying the resonant frequency of the cavity system, said electron means including said second cathode connected to a source of direct current potential for forming an electron cloud in the interspace between second cathode and upper edges of said radial vanes.

3. An electron discharge device for generating high frequencies having a first cathode, a single anode and an associated resonant system within a vacuum space having radial inwardly projecting vanes in cooperative relation with said first cathode, means for varying the frequency of said resonant system, said means including a second cathode in cooperative relation with a portion of said radial vanes, and a source of potential connected to said second cathode, whereby an electron cloud is formed in the high frequency eld between the second cathode and the inner edges of said vanes.

4. An oscillation generator of the multicavity magnetron type having a first cathode and a single cylinder anode coaxial with the cathode and having a plurality of inwardly projecting members extending axially beyond said first cathode and with lateral interspaces forming resonant cavities, means for varying the resonant frequency of said cavities, said means including a second cathode coaxial with the rst cathode and in cooperative relation with said axially extending members and a source of direct current potential connected to said second cathode whereby an electron cloud is formed in the interspace between the second cathode and said axially extending members.

5. An oscillation generator of the multicavity magnetron type having a, rst cathode and a single anode with a plurality of resonant cavities whose inwardly projecting edges are coaxial with the cathode and extend axially beyond said first cathode, electron means for varying the resonant frequency of said cavities, said means including a second cathode coaxial with nrst cathode in cooperative relation with said axially extending edges, and a source of direct current connected to the second cathode whereby an electron cloud is formed in the eld between the second cathode and said axially extending edges.

6. An oscillation generator of the multicavity magnetron type having first and second cathodes aligned on the same axis, a single anode having a plurality of resonant cavities with inwardly projecting edges coaxial with and in cooperative relation with said cathodes, said rst cathode connected to a source of high direct current potential for generating high frequency oscillations in said resonant cavities, and a second source of direct current potential connected to the second cathode whereby an electron cloud is formed in the interspace between second cathode and a portion of said inwardly projecting edges for varying the resonant frequency of said cavities.

ALBERT M. CLOGSTON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,149,024 Lindenblad Feb. 28, 1939 2,171,212 Hollman Aug. 29, 1939 2,217,447 Mouromtseff et al. Oct. 8, 1940 2,413,385 Schmidt Dec. 31, 1946 2,414,085 Hartman Jan. 14, 1947 2,446,531 Derby Aug. 10, 1948 2,463,512 Brown Mar. 8, 1949 2,468,183 Derby Apr. 26, 1949 2,468,243 Spencer Apr. 26, 1949 

